Unitary series spark gap with aligned apertures

ABSTRACT

A spark-gap device includes first and second pairs of conductive electrodes supported within first and second insulating spacer means to provide first and second gaps. The gaps are connected in series by joining the rearward portion of one electrode of the first pair to the rearward portion of one electrode of the second pair. The joined electrodes are hollow to provide a chamber therebetween, and are apertured so that an arc discharge at one gap provides illumination of the second gap. As a result of illumination of one gap by a discharge at the other, the gaps break down at substantially the same time. Furthermore, the chamber between the gaps aids in rapidly extinguishing an arc at the first current zero after an overvoltage condition subsides.

United States Patent 191 Kawiecki Feb. 11,1975

1 1 UNITARY SERIES SPARK GAP WITH ALIGNED APERTURES [73] Assignee:Joslyn Mtg. and Supply Co.,

Chicago, 111.

[22] Filed: Nov. 12, 1973 [21] Appl. No.: 414,858

Related US Application Data [63] Continuation of Ser. No. 298,014, Oct.16, 19 72,

abandoned.

[52] US. Cl 315/203, 313/325, 317/69 [51] Int. Cl. H05b 41/14 [58] Fieldof Search 315/36, 189; 313/196, 217, 313/220, 325, 203, 311, 306, 268,257

Primary ExaminerNathan Kaufman Attorney, Agent, or Firml(larquist,Sparkman, Campbell, Leigh, Hall & Whinston [57] ABSTRACT A spark-gapdevice includes first and Second pairs of conductive electrodessupported withinfirst and second insulating spacer means to providefirst and second gaps. The gaps are connected in series by joining therearward portion of one electrode of the first pair to the rearwardportion of one electrode of the second pair. The joined electrodes arehollow to provide a chamber therebetween, and are apertured so that anarc discharge at one gap provides illumination of the second gap. As aresult of illumination of one gap by a discharge at the other, the gapsbreak down at substantially the same time. Furthermore, the chamberbetween the gaps aids in rapidly extinguishing an are at the firstcurrent zero after an overvoltage condition subsides.

15 Claims, 5 Drawing Figures PAIENIED 3.866.091

v CHESTER J. KAWIECKI INVENTOR BUCKHORN, BLORE, KLARQUIST & SPARKMANATTORNEYS UNITARY SERIES SPARK GAP WITH ALIGNED APERTURES This is acontinuation of application Ser. No. 298,014 filed Oct. 16, l972, nowabandoned.

BACKGROUND OF THE INVENTION Spark-gap devices are frequently employed astransient protectors across voltage supply lines for protectingelectrical equipment from transient surges. For example, such aspark-gap device may be employed as a lightning arrestor providing abreakdown path from line to line, or line to ground, when a lightningsurge occurs. Therefore the surge does not reach and destroy electricalequipment also connected to the line.

It would be desirable to provide protection at a voltage not much higherthan rated line voltage, with discontinuance of the short circuitsubstantially immediately after the overvoltage condition subsides. Thatis, a spark-gap device on an alternating current system shouldextinguish the arc by the time of the first current zero after a linesurge disappears. By way of example, a spark-gap device set to provide adischarge when the line voltage reaches 350 volts peak should extinguishwhen the line voltage returns to a 170 volt peak, or I volt R.M.S., linevoltage. Unfortunately, the ordinary gap set for such a low breakdownvoltage would restrike in response to the normally impressed operatingvoltage resulting in failure of the spark-gap device. Consequently, aspark-gap device must ordinarily be set for quite a high breakdownvoltage if itis to extinguish at normal operating voltages.

SUMMARY OF THE INVENTION Briefly, in accordance with the presentinvention a spark-gap device includes first and second pairs ofspark-gap electrodes connected in series. The-device is constructed suchthat an arc discharge across one gap causes illumination of the othergap whereby the two gaps break down substantially simultaneously uponthe occurrence of an overvoltage condition thereacross. Furthermore, anenclosed chamber communicates with the gaps to promote extinguishing ofthe arc discharge after the cessation of the overvoltage condition. Inaccordance with a preferred embodiment, one electrode of each pair isapertured, and the apertured electrodes are joined for providing apassage therethrough acting not only to establish illumination of onegap by the other, but also providing an enclosed chamber which promotesextinguishing of an arc discharge after the overvoltage condition isremoved.

It is accordingly an object of the present invention to provide animproved spark-gap device for furnishing enhanced overvoltageprotection.

It is another object of the present invention to provide an improvedspark-gap device which will break down and protect a voltage supply lineat a comparatively low overvoltage value, and which will extinguish thearc at the cessation of such overvoltage condition.

The present invention, both as to organization and method of operation,together with further advantages and objects thereof may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings wherein like reference characters referto like elements.

DRAWINGS FIG. 1 is a side view ofa spark-gap device according to thepresent invention as supported in a holder;

FIG. 2 is a circuit diagram illustrating application of a spark-gapdevice according to the present invention;

FIG. 3 is an enlarged longitudinal cross section of a spark-gap deviceaccording to the present invention;

FIG. 4 is an enlarged longitudinal cross section of an extendedspark-gap device according to the present invention; and

FIG. 5 is a transverse cross sectional view of the FIG. 1 spark-gapdevice taken at 5-5 in FIG. 4.

DETAILED DESCRIPTION Referring to the drawings, and particularly toFIGS. 1 and 3, a spark-gap according to the present invention includescylindrical spacer tubes 10 and 12 preferably taking the form of ceramictubes. The device is quite small, and each of the cylindrical spacertubes may be approximately 5/16 inch in diameter and approximately 5/16inch in length. The spacer tubes are most clearly shown in FIG. 3wherein the spark-gap device according to the present invention isillustrated in greatly enlarged cross section. In assembling thesparkgap device according to the present invention, the ends of aceramic spacer tube, for example tube 10, are suitably metalized asindicated at 14 and 16 with a high temperature metal or alloy, i.e.molybdenum plus manganese. Brazing washers l8 and 20, which may beformed of an alloy of silver and copper, are suitably positioned uponthe metalized ends. Then, thin-walled hollow electrodes 22 and 24 areinserted into either end of ceramic tube 10, each of these electrodesbeing substantially cylindrical in shape. For example, electrode 22 hasa first inner length 26 having a first diameter, and a second or outerlength 28 of a larger diameter which approaches the inside diameter ofceramic tube 10. The electrode is also provided with an annular flange30 at its outer end for making contact with brazing washer 18. Betweenlength 26 and length 28 of the electrode, the diameter thereof changesgradually to provide a flared configuration, or a configuration adaptedto provide a bellows" action between the electrode and the ceramicspacer tube as when thermal expansion and contraction of the memberstake place. The thin-walled hollow electrodes 22 and 24 are preferablyformed of Kovar, and the ceramic spacer tubes are preferably alumina. Achamber 32 is provided by the above construction between tube 10 andelectrodes 22 and 24.

The spark-gap device also includes hollow electrodes 34 and 36,substantially identical to electrodes 22 and 24, respectively, which areinserted within spacer tube 12. As in the case of joining electrodes 22and 24 to spacer tube 10 to provide chamber 32, joinder of electrodes 34and 36 to tube 12 provides interior chamber 42. Ceramic tube 12 ismetalized as indicated at 58 and 60, while brazing washers 62 and 64 arelocated between the spacer tube and the respective electrodes. Thematerials employed for electrodes and for brazing elements are suitablythe same as hereinbefore described in connection with electrodes 22 and24, and tube 10.

Hollow electrodes 24 and 36 are juxtaposed, and a further brazing washer38 is included in the assembly between the flanges of electrodes 24 and36 whereby these electrodes are joined together in a series circuit.There is thereby also formed a chamber 40 substantially separate fromthe region of the gaps within and between the hollow electrodes 24 and36.

Electrodes 22 and 24 include end portions or end walls 44 and 46 whichface one another and define a first gap 48 therebetween. Electrode endwall 44 is suitably slightly cup-shaped or concave where it faceselectrode 46 for the reception of a deposit of low work functionmaterial. Similarly, electrodes 34 and 36 have end portions or end walls50 and 52 which face one another to define a gap 54 therebetween, andelectrode 34 is suitably cup-shaped. The end walls 46 and 52 ofelectrodes 24 and 36 are respectively provided with apertures 55 and 56centrally facing the gap region which provide communication betweenchamber 40 and the region of the gaps, and which are aligned so thatillumination taking place at one gap will also'illuminate the oppositegap. No other communication besides apertures 55 and 56 is desirablebetween chambers 32, 40, and 42.

To secure the various electrodes within spacer tubes and 12, theassembly of components as described, with brazing washers in place, israised in temperature to braze the assembly. The interiors of thechambers are evacuated and suitably provided with an internal gaseousenvironment at less than atmospheric pressure. The chambers 32, 40, and42 are hermetically sealed, and communicate only with one anotherthrough aper tures 55 and 56.

The spark-gap device according to the present invention is suitablysupported and connected to circuitry to be protected employing a holdergenerally indicated at including spring clips 68 and 70 joined atinsulated base 72 as illustrated in FIG. 1. Spring clips 68 and 70terminate in caps 74 and 76, shown in cross section in FIG. 1, employedfor engaging the end flanges of the spark-gap 'device. The spring clips68 and 70 are adapted to urge the caps against the end flanges to makegood contact therewith, but are not required to form a hermeticallysealed contact.

A spark-gap according to the present invention is connected to a line tobe protected or between a line and ground by means of spring clips 68and 70. A connection for a spark-gap device 78 according to the presentinvention is illustrated in FIG. 2 where end terminals thereof areconnected respectively to voltage supply lines 80 and 82 extending froma source of power to a load 84. When a predetermined voltage level isreached, e.g. as a result of a high voltage transient .on the line, gaps48 and 54 break down into an arc discharge, thereby shorting out thehigh voltage transient, and protecting load 84 and other equipment onthe line. The gaps 48 and 54 are suitably spaced such and thepressurization within the spark-gap device is predetermined such that anarc discharge occurs across gaps 48 and 54 at a relatively lowovervoltage value. To use the previous example, spark-gap device 78 maybe set to break down at an overvoltage condition of 350 volts peakacross a line where the operating voltage is I volts R.M.S. orapproximately I70 volts peak. Since the gaps 48 and 54 are connected inseries, an arc discharge takes place across both gaps at approximatelythe same time. However, except for the passage? provided by apertures'55and 56 and chamber 40, there would be an excessive time lag beforecompletion of an arc discharge. Both gaps would have to fire separatelyand their respective time lags would add. With the present device,substantially simultaneousionization takes place at both gaps as aresult ofthe passage formed by apertures 55 and 56, and chamber 40. Notonly does direct gas ionization take place through the passage,

but also the initiation of an arc discharge across one gap providesradiation illuminating the region of the other gap. This illuminationproduces photoelectrons at an electrode of the opposite gap,.which inturn cause ionization of the gas in the region of such gap. For example,assuming gap 54 is the first to break down, the

arc discharge at gap 54 will illuminate end portion 44 of electrode 22through apertures 56 and 55. The photons reaching portion 44 willproduce photoelectrons which will be emitted from portion 44 and which,in turn, will cause ionization of gap 48. As aresult, gap 48 breaks downsubstantially immediately into an are discharge. The time lag duringwhich the foregoing events take place is such that both gapsbreak downat substantially the same time. The terms illumination and radiationemployed above are meant to comprehend ultraviolet and/or visibleradiation.

A further important advantage of the present invention relates toextinguishing of the arc discharge when an overvoltage'condition isremoved. For example, assume the voltage between voltage supply linesand 82 in FIG. 2 drops from an overvoltage of 350 volts peak to a normal170 volts peak for a volt supply line. At the occurrence of the nextcurrent zero, that is, when the alternating current wave next passesthrough the zero axis, the arc extinguishes at each of the gaps. Thearcs do not then restrike as the line voltage again rises to a normalvolts peak value. By wayof explanation, it will be noted that threeseparate gas chambers are provided within the device of the presentinvention, namely, chambers 32, 40, and 42. The three separate gaschambers appear to break up the ionized gas channel,.causing fasterdeionization at the end of an overvoltage condition. Moreover,-the gasin chamber 40, communicating with the region of the gaps, is muchcooler, and not ionized to the same degree as the gases in chambers32and 42. At the occurrence of the first current zero after anovervoltage condition is removed, the ionized gas appears to. bereplaced or intermixed with cooler gas through apertures 55 and 56whereby the gaps do not restrike. The above explanations are postulatedas possible reasons why the present construction is efficacious inextinguishing a discharge after an overvoltage condition is passed, andit is understood the invention is not limited to any given theory ofoperation.

The construction according to the present invention may be expanded asillustrated in FIG. 4 wherein a spark-gap device includes fourindividual gap devices, 86, 88, 90, and 92 joined ina seriesconstruction. This configuration is suitable for higher voltageapplications than would be the double 'gap illustrated in FIGS. 1 and 3.Construction and operation are substantially the same as hereinbeforedescribed in connection with the embodiment of FIGS. 1 and 3. Allelectrodes except the end electrodes are apertured to provideinterconnecting chambers between gaps, as well as a passage for theillumination of the several gaps'by a first gap to break down, wherebydischarge will then substantially take place at all gaps. FIG. 5 is across sectional view taken at 5--5 in FIG. 4, and illustrates aperture56 in electrode 36. The same cross section is equally illustrative ofthe device of FlGS. l and 3.

There is provided according to the present invention a small sizespark-gap device which is suitably constructed to break down and providean arc discharge at a relatively low transient voltage value, forexample, at a value just above the normal peak voltage value occurringacross a protected line. In the example given, the breakdown voltage wasapproximately twice the normal peak voltage across the protected linehAtthe-conclusion of a high voltage transient, the spark-gap deviceaccording to the present invention substantially immediatelyextinguishes the'arc, that is, the arc is extinguished at the occurrenceof the next current Zero of the alternating current wave and does notrestrike.

The device according to the present invention is susceptible tovariation without departing from the inventive concept. For example,although spark-gap device 78 in FIG. 2 is illustrated as being connectedacross a line, without connection of the floating electrodes indicatedat 94, it is understood that such interconnection may in some instancesbe grounded. It is preferred, however, that a construction such asillustrated in FIG. 4 be employed in such instance, wherein centerconnection ,96 is grounded with end connections of the device disposedacross a voltage supply line.

Moreover, any number of individual gap devices may be arranged in aseries construction of the type illustrated in FIG. 4, with four suchdevices being given only by way of example. 1

While 1 have shown and described preferred embodiments of my invention,it will be apparent to those skilled in the art that many other changesand modifications may be made without departing frommy invention in itsbroader aspects. I therefore intend the appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof my invention.

I claim:

1. A spark-gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

a first pair of conductive electrodes,

insulating spacer means positioning said first pair of electrodes withopposed portions thereof in facing relation for defining a first gaptherebetween adapted to break down and support an arc discharge,

a second pair of conductive electrodes,

insulating spacer means positioning said second pair of electrodes withopposed portions thereof in facing relation for defining a second gaptherebetween adapted to break down and support an arc discharge,

one of said second pair of electrodes being electrically connected toone of said first pair of electrodes for providing a seriescircuit-including said gaps, said device being constructed so that anarc discharge across one gap causes illumination of the other gap,

and a first enclosed chamber substantially separate from the region ofsaid gaps and communicating with the region of said gaps to promoteextinguishing of an arc discharge across the said gaps after thecessation of an over-voltage condition across said gaps in series,

wherein said insulating spacer means cooperate with said electrodes toenclose the first and second gaps in second and third separate chambersrespectively, said insulating spacer means being joined to therespective pairs of electrodes with which they form chambers tohermetically seal said second and third chambers except forcommunication with said first chamber.

2. The device according to claim 1 wherein the connected electrodes arehollow and are joined to provide said first enclosed chamber which' ishermetically sealed except for communicationv with said second and thirdchambers,

said connected electrodes being provided with apertures through portionsthereof adjacent said gaps to communicate with said gaps.

3. The device according to claim 2 wherein said electrodes arelongitudinally aligned so that said apertures in said connectedelectrodes provide a line-of-sight path between opposed portions of theremaining electrodes.

4. A spark-gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

a first hollow enclosure means provided with a first pair of alignedconductive electrodes extending into said first hollow enclosure meansand completing a first chamber therewith, said first pair of electrodeshaving adjacent opposed portions defining a first gap therebetweenwithin said first chamber,

and a second hollow enclosure means provided with a second pair ofaligned conductive electrodes extending into said second enclosure meansand completing a second chamber therewith, said second pair ofelectrodes having adjacent opposed portions defining a second gaptherebetween within said second chamber,

one electrode of said first pair and one electrode of said second pairbeing connected to provide a series electrical circuit including saidgaps,

said connected electrodes being provided with a direct passage betweensaid first and second gaps for providing illumination of at least aportion of one of said gaps by an arc discharge occurring across theother of said gaps, said passage comprising a third chambercommunicating with the region of the gaps in said first and secondchambers,

said hollow enclosure means being joined to the respective electrodesthey enclose the hermetically seal said first and second chambers exceptfor communication with said third chamber.

5. The device according to claim 4 wherein said connected electrodes arehollow and are sealed back-toback to hermetically seal said thirdchamber except for communication .with said first and second chambers,said connected electrodes being centrally apertured at said gaps tocomplete said direct passage.

6. The device according to claim 4 wherein said enclosure means comprisespacer means and wherein said spacer means and said electrodes aresubstantially cylindrical, hollow, and aligned, each electrode having anend portion adjacent and forming an arc-supporting surface of one ofsaid gaps within: a respective spacer means, a first length of each suchelectrode next to the end portion having a first diameter, a secondlength of such electrode having a second and larger diameter where suchelectrode is provided with an annular flange joined to an end of arespective spacer member, and a third length of changing diameterjoining said first and second lengths, said connected electrodes beingjoined at their annular flanges in substantial alignment to formsaid'third chamber therewithin and being centrally apertured at saidgaps to complete said direct passage.

7. The device according to claim 6 wherein said spacer members areformed of ceramic, with said annular flange of each said electrode beingbrazed to an end of a spacer member, and wherein the annular flanges ofsaid connected electrodes are brazed together.

8. The device according to claim 4 wherein said connected electrodes aresubstantially aligned and hollow,

extending longitudinally within the respective enclosure means to formsaid third chamber, and are provided with apertures where they face theremaining electrodes to complete said passage, said apertures providinga line-of-sight path between facing portions of the remaining electrodesand communication with said third chamber.

9. The device according to claim 1 wherein said connected electrodesprotrude within the respective spacer means while being joined toprovide said first enclosed chamber, said connected electrodes'beingprovided with aligned apertures adjacent said gaps.

10. A spark gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

a first hollow enclosure means provided with a first pair of alignedconductive electrodes extending into said first hollow enclosure meansand completing a first chamber therewith, said first pair of electrodeshaving adjacent opposed portions defining a first gap therebetweenwithin said first chamber.

and a second hollow enclosure means provided with a second pair ofaligned conductive electrodes extending into said second enclosure meansand completing a second chamber therewith, said second pair ofelectrodes having adjacent opposed portions defining a second gaptherebetween within said second chamber,

one electrode of said first pair and one electrode of said second pairbeing unitary to provide a series electrical circuit including saidgaps,

said one electrode of said first pair and said one electrode of saidsecond pair being provided with a direct passage between said first andsecond gaps for providing illumination of at least a portion of one ofsaid gaps by an arc discharge occurring across the other of said gaps,

said hollow enclosure means being joined to the respective electrodesextending therewithin to hermetically seal said first and secondchambers except for said direct passage.

11. A spark gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

a first hollow enclosure means provided with a first pair of alignedconductive electrode means completing a first chamber therewith, saidfirst pair of electrode means having adjacent opposed portions defininga first gap therebetween within said first ond hollow enclosure means,said second pair of electrode means having adjacent opposed portionsdefining a second gap therebetween within-said second chamber,

one electrode means of said first pair being unitary with one electrodemeans of said second pair, the remaining electrode means of said pairsextending into the respective hollow enclosure means,

said unitary electrode means being provided with a direct passagebetween said first and second gaps for providing illumination of atleast a portion of one of said gaps by an arc discharge occurring acrossthe other of said gaps,

said hollow enclosure means being joined to the respective electrodemeans with which they commplete a chamber to hermetically seal saidfirst and second chambers except for said direct passage.

12. A spark gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

first and second aligned conductive electrode means, and a first hollowenclosure means therebetween completing a first chamber with said firstand second electrode means, said first and second electrode means havingadjacent opposed portions defining a first gap therebetween within saidfirst chamber, said first conductive electrode means extending into saidfirst hollow enclosure means,

a third electrode means aligned with the first and second electrodemeans, and a second hollow enclosure means between the second and thirdelectrode means completing a second chamber with the second and thirdelectrode means, said second and third electrode means having adjacentopposed portions defining a second gap therebetween within said secondchamber, saidthird conductive electrode means extending into said secondhollow enclosure means,

said second electrode means being provided with a direct passage betweensaid first and second gaps for providing illumination of at least aportion of one of said gaps by the arc discharge occurring across theother of said gaps,

said hollow enclosure means being joined to the re spective electrodemeans with which they complete a chamber to hermetically seal saidfirst'and second chambers except for said direct passage.

13. The device according to claim 12 wherein said first and thirdelectrode means are disposed in juxtaposed facing spaced relation in thelongitudinal direc-.

tion ofsaid device, with the second electrode means forming a barriertherebetween except for said direct passage, said first and second gapsbeing formed between lateralv exposed faces of said second electrodemeans and the said'first and third electrode means respectively.

14. The device according to claim 12 wherein said enclosure meanscomprise spacer means and are substantially cylindrical, hollow, andaligned, said electrode means extending within said enclosure means alsobeing substantially hollow andaligned, each having an end portionadjacent and forming an arc supporting surface of one of said gapswithin a respective enclosure means, and each being provided with anannular flange joined to an end of the respective enclosure means.

15. A spark-gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising:

a first hollow enclosure means provided with a first pair of alignedconductive electrodes extending into said first hollow enclosure meansand completing a first chamber therewith, said first pair of electrodeshaving adjacent opposed portions defining a first gap therebetweenwithin said first chamber,

a second hollow enclosure means provided with a second pair of alignedconductive electrodes extending into said second enclosure means andcompleting a second chamber therewith, said second pair of electrodeshaving adjacent opposed portions defining a second gap therebetweenwithin said second chamber,

one electrode of said first pair and .one electrode of said second pairbeing connected to provide a series electrical-circuit including saidgaps,

said connected electrodes being substantially aligned and hollow,extending longitudinally within the respective enclosure means to form athird chamber,

and further enclosure means and further electrodes extending therewithinin longitudinal alignment with said first and second enclosure means forproviding further gaps in further chambers,

each electrode being apertured except for end electrodes, and with therearward portion of each electrode being joined to the next except forend electrodes,

said apertures providing a direct line-of-sight passage between gaps forproviding illumination therebetween when an arc discharge occurs acrossat least one of said gaps,

said hollow enclosure means being joined to the respective electrodesthey enclose to hermetically seal the chambers formed thereby except forcommunication between chambers provided by said apertures.

1. A spark-gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising: afirst pair of conductive electrodes, insulating spacer means positioningsaid first pair of electrodes with opposed portions thereof in facingrelation for defining a first gap therebetween adapted to break down andsupport an arc discharge, a second pair of conductive electrodes,insulating spacer means positioning said second pair of electrodes withopposed portions thereof in facing relation for defining a second gaptherebetween adapted to break down and support an arc discharge, one ofsaid second pair of electrodes being electrically connected to one ofsaid first pair of electrodes for providing a series circuit includingsaid gaps, said device being constructed so that an arc discharge acrossone gap causes illumination of the other gap, and a first enclosedchamber substantially separate from the region of said gaps andcommunicating with the region of said gaps to promote extinguishing ofan arc discharge across the said gaps after the cessation of anover-voltage condition across said gaps in series, wherein saidinsulating spacer means cooperate with said electrodes to enclose thefirst and second gaps in second and third separate chambersrespectively, said insulating spacer means being joined to therespective pairs of electrodes with which they form chambers tohermetically seal said second and third chambers except forcommunication with said first chamber.
 2. The device according to claim1 wherein the connected electrodes are hollow and are joined to providesaid first enclosed chamber which is hermetically sealed except forcommunication with said second and third chambers, said connectedelectrodes being provided with apertures through portions thereofadjacent said gaps to communicate with said gaps.
 3. The deviceaccording to claim 2 wherein said electrodes are longitudinally alignedso that said apertures in said connected electrodes provide aline-of-sight path between opposed portions of the remaining electrodes.4. A spark-gap device suitable for providing transient protection to aline above a predetermined voltage level, said device comprising: afirst hollow enclosure means provided with a first pair of alignedconductive electrodes extending into said first hollow enclosure meansand completing a first chamber therewith, said first pair of electrodeshaving adjacent opposed portions defining a first gap therebetweenwithin said first chamber, and a second hollow enclosure means providedwith a second pair of aligned conductive electrodes extending into saidsecond enclosure means and completing a second chamber therewith, saidsecond pair of electrodes having adjacent opposed portions defining asecond gap therebetween within said second chamber, one electrode ofsaid first pair and one electrode of said second pair being connected toprovide a series electrical circuit including said gaps, said connectedelectrodes being provided with a direct passage between said first andsecond gaps for providing illumination of at least a portion of one ofsaid gaps by an arc discharge occurring across the other Of said gaps,said passage comprising a third chamber communicating with the region ofthe gaps in said first and second chambers, said hollow enclosure meansbeing joined to the respective electrodes they enclose the hermeticallyseal said first and second chambers except for communication with saidthird chamber.
 5. The device according to claim 4 wherein said connectedelectrodes are hollow and are sealed back-to-back to hermetically sealsaid third chamber except for communication with said first and secondchambers, said connected electrodes being centrally apertured at saidgaps to complete said direct passage.
 6. The device according to claim 4wherein said enclosure means comprise spacer means and wherein saidspacer means and said electrodes are substantially cylindrical, hollow,and aligned, each electrode having an end portion adjacent and formingan arc-supporting surface of one of said gaps within a respective spacermeans, a first length of each such electrode next to the end portionhaving a first diameter, a second length of such electrode having asecond and larger diameter where such electrode is provided with anannular flange joined to an end of a respective spacer member, and athird length of changing diameter joining said first and second lengths,said connected electrodes being joined at their annular flanges insubstantial alignment to form said third chamber therewithin and beingcentrally apertured at said gaps to complete said direct passage.
 7. Thedevice according to claim 6 wherein said spacer members are formed ofceramic, with said annular flange of each said electrode being brazed toan end of a spacer member, and wherein the annular flanges of saidconnected electrodes are brazed together.
 8. The device according toclaim 4 wherein said connected electrodes are substantially aligned andhollow, extending longitudinally within the respective enclosure meansto form said third chamber, and are provided with apertures where theyface the remaining electrodes to complete said passage, said aperturesproviding a line-of-sight path between facing portions of the remainingelectrodes and communication with said third chamber.
 9. The deviceaccording to claim 1 wherein said connected electrodes protrude withinthe respective spacer means while being joined to provide said firstenclosed chamber, said connected electrodes being provided with alignedapertures adjacent said gaps.
 10. A spark gap device suitable forproviding transient protection to a line above a predetermined voltagelevel, said device comprising: a first hollow enclosure means providedwith a first pair of aligned conductive electrodes extending into saidfirst hollow enclosure means and completing a first chamber therewith,said first pair of electrodes having adjacent opposed portions defininga first gap therebetween within said first chamber. and a second hollowenclosure means provided with a second pair of aligned conductiveelectrodes extending into said second enclosure means and completing asecond chamber therewith, said second pair of electrodes having adjacentopposed portions defining a second gap therebetween within said secondchamber, one electrode of said first pair and one electrode of saidsecond pair being unitary to provide a series electrical circuitincluding said gaps, said one electrode of said first pair and said oneelectrode of said second pair being provided with a direct passagebetween said first and second gaps for providing illumination of atleast a portion of one of said gaps by an arc discharge occurring acrossthe other of said gaps, said hollow enclosure means being joined to therespective electrodes extending therewithin to hermetically seal saidfirst and second chambers except for said direct passage.
 11. A sparkgap device suitable for providing transient protection to a line above apredetermined voltage level, said device comprising: a first hollowenclosure means provided with a first pair Of aligned conductiveelectrode means completing a first chamber therewith, said first pair ofelectrode means having adjacent opposed portions defining a first gaptherebetween within said first chamber, and a second hollow enclosuremeans provided with a second pair of aligned conductive electrode meanscompleting a second chamber with said second hollow enclosure means,said second pair of electrode means having adjacent opposed portionsdefining a second gap therebetween within said second chamber, oneelectrode means of said first pair being unitary with one electrodemeans of said second pair, the remaining electrode means of said pairsextending into the respective hollow enclosure means, said unitaryelectrode means being provided with a direct passage between said firstand second gaps for providing illumination of at least a portion of oneof said gaps by an arc discharge occurring across the other of saidgaps, said hollow enclosure means being joined to the respectiveelectrode means with which they commplete a chamber to hermetically sealsaid first and second chambers except for said direct passage.
 12. Aspark gap device suitable for providing transient protection to a lineabove a predetermined voltage level, said device comprising: first andsecond aligned conductive electrode means, and a first hollow enclosuremeans therebetween completing a first chamber with said first and secondelectrode means, said first and second electrode means having adjacentopposed portions defining a first gap therebetween within said firstchamber, said first conductive electrode means extending into said firsthollow enclosure means, a third electrode means aligned with the firstand second electrode means, and a second hollow enclosure means betweenthe second and third electrode means completing a second chamber withthe second and third electrode means, said second and third electrodemeans having adjacent opposed portions defining a second gaptherebetween within said second chamber, said third conductive electrodemeans extending into said second hollow enclosure means, said secondelectrode means being provided with a direct passage between said firstand second gaps for providing illumination of at least a portion of oneof said gaps by the arc discharge occurring across the other of saidgaps, said hollow enclosure means being joined to the respectiveelectrode means with which they complete a chamber to hermetically sealsaid first and second chambers except for said direct passage.
 13. Thedevice according to claim 12 wherein said first and third electrodemeans are disposed in juxtaposed facing spaced relation in thelongitudinal direction of said device, with the second electrode meansforming a barrier therebetween except for said direct passage, saidfirst and second gaps being formed between lateral exposed faces of saidsecond electrode means and the said first and third electrode meansrespectively.
 14. The device according to claim 12 wherein saidenclosure means comprise spacer means and are substantially cylindrical,hollow, and aligned, said electrode means extending within saidenclosure means also being substantially hollow and aligned, each havingan end portion adjacent and forming an arc supporting surface of one ofsaid gaps within a respective enclosure means, and each being providedwith an annular flange joined to an end of the respective enclosuremeans.
 15. A spark-gap device suitable for providing transientprotection to a line above a predetermined voltage level, said devicecomprising: a first hollow enclosure means provided with a first pair ofaligned conductive electrodes extending into said first hollow enclosuremeans and completing a first chamber therewith, said first pair ofelectrodes having adjacent opposed portions defining a first gaptherebetween within said first chamber, a second hollow enclosure meansprovided with a second pair of aligned conductive electrodes Extendinginto said second enclosure means and completing a second chambertherewith, said second pair of electrodes having adjacent opposedportions defining a second gap therebetween within said second chamber,one electrode of said first pair and one electrode of said second pairbeing connected to provide a series electrical circuit including saidgaps, said connected electrodes being substantially aligned and hollow,extending longitudinally within the respective enclosure means to form athird chamber, and further enclosure means and further electrodesextending therewithin in longitudinal alignment with said first andsecond enclosure means for providing further gaps in further chambers,each electrode being apertured except for end electrodes, and with therearward portion of each electrode being joined to the next except forend electrodes, said apertures providing a direct line-of-sight passagebetween gaps for providing illumination therebetween when an arcdischarge occurs across at least one of said gaps, said hollow enclosuremeans being joined to the respective electrodes they enclose tohermetically seal the chambers formed thereby except for communicationbetween chambers provided by said apertures.